1930s house, mortar is falling out like sand under DPC!!

[vespa]

the bricks in our house are defiantly not glazed (the houses weren't built very well), i remember the ones you mean though, the basement in my old junior school had them, dark brown i think they were

You can't go wrong with a 1:1:4 mix using lime. Pictures and DPC method would be a plus so people could advise you better. No need to wet the wall any more by the way, just give it a good brush down. A damp wall will not have a high suction so just brush down. Walls damp enough...